The present invention relates to functional organic compounds, and more particularly, to novel pyran derivatives which are useful in photochemical polymerization, dye laser, and electroluminescence.
After coming into this information age, photochemical polymerization has been frequently used in a variety of fields, and beyond the bounds of the field of synthetic resins, it is being extensively used in other fields of information recordings and electric equipments such as paints, plates for printings, printing circuits, integrated circuits, etc. Photochemical polymerization, a technique for polymerizing polymerizable compounds by irradiating light, is classified roughly into photopolymerization where polymerizable compounds are initiated to be polymerized and activated by directly irradiating light, an photosensitizing polymerization where polymerizable compounds are polymerized by irradiating light in the presence of photosensitizers to form growth active-cores of photosensitizers. The photochemical polymerizations have characteristics that the initiation and suspension of polymerization can be controlled by flashing excitation light, and the polymerization rate and degree can be easily controlled by selecting the strength and wavelength of excitation. Photochemical polymerization can be proceeded even at relatively-low temperatures because its polymerization-initiating-energy is relatively low.
At present, owing to the above characteristics of photopolymerization, there are rapidly arising demands for photopolymerizable compositions, which can be polymerized by irradiating visible light such as argon ion lasers, helium/neon lasers, and second harmonic of YAG lasers, with the development of new information recordings such as plates for printings and holographs. However, since conventional polymerizable compounds and polymerization initiators to be incorporated in photopolymerizable compositions selectively absorb ultraviolet rays, photopolymerizable compositions inevitably require photosensitizers as an essential technical factor when they are polymerized by irradiating visible light. Accordingly, in photopolymerizable compositions used in information recordings and electric equipments, polymerizable compounds should be used in combination with photosensitizers, polymerization initiators, binding resins, etc., which are all selected from various materials dependently on their uses. In general, methods comprising the steps of selecting materials for polymerizable compounds and/or polymerization initiators other than photosensitizers, and then screening photosensitizers which may appropriately sensitize the selected materials through trials and errors.
The characteristics required in photosensitizers are a relatively-large molecular extinction coefficient in the visible region; an ability of sensitizing polymerizable compounds and polymerization initiators; a higher sensitization efficiency; a superior solubility in solvents and compatibility with other components; and a satisfactory stability. Such photosensitizers include, for example, merocyanine dyes as disclosed in Japanese Patent Kokai No. 151,024/79, cyanine dyes as disclosed in Japanese Patent Kokai No. 29,803/83, stilbene derivatives as disclosed in Japanese Patent Kokai No. 56,403/84, coumarin derivatives as disclosed in Japanese Patent Kokai No. 23,901/88, pyran derivatives as disclosed in Japanese Patent Kokai No. 329,654/94, and methylene blue derivatives as disclosed in Japanese Patent Kokai No. 33,104/89. These photosensitizers, however, have unignorable disadvantages and remarkable advantages. There has been found no photosensitizer which consistently exerts the above characteristics in photo-polymerizable compositions containing appropriate materials.
Organic compounds sensitive to light, particularly, luminescent organic compounds are useful in the field of dye lasers and electroluminescence.
In the field of dye lasers, as disclosed, for example, by Kaoru IGARASHI in xe2x80x9cShikizai-Kyokai-shixe2x80x9d, Vol. 70, No. 2, pp. 102-111 (1997), compounds which give luminescence in the visible region have been eagerly screened since the report of dye laser""s lasing in 1960""s. As the progress of information recording technology, there are arising demands for compounds which give luminescence in a longer wavelength region, more particularly, in the visible region.
In the field of information displays, electro-luminescent devices (hereinafter abbreviated as xe2x80x9cEL devicesxe2x80x9d) are highlighted as displaying devices for the forthcoming generation. Nowadays, cathode-ray tubes are predominantly used in a relatively large size of information displaying means such as computer termini and TV receivers. The cathode-ray tubes are, however, relatively large in mass and weight and relatively high in operation voltage, thus the tubes are inadequate for consumer""s equipments and small-sized equipments where portability is an important factor. In the small-sized equipments, display devices which have a depthless, light and plain form; and operate at a relatively-low operation voltage and wattage, are required. Because of the advantageous characteristics of a relatively-low operation voltage and wattage, liquid crystal devices are now widely used in various fields. However, because the contrast changes depending on view angles in the information displaying means using the liquid crystal devices, informations can be clearly displayed only when viewed within a specific view angle and the wattage is not effectively reduced as much as expected because they generally need backlight. A device, which is now focused as a displaying device for overcoming the drawbacks as described above, is an organic electro-luminescent device or an organic EL device.
Organic EL device is a luminescent device which is formed by inserting a thin layer containing a luminescent agent between a cathode and an anode, and which utilizes luminescence such as fluorescence or phosphorescence emitted by the luminescent agent when a dc voltage is first supplied between the cathode and the anode to supply positive holes and electrons to the thin layer and to rebind the positive holes and the electrons in order to bring the luminescent agent into an excited state, and then the excited agent returns to the ground state. As a characteristic, organic EL device is appropriately changeable its luminous color tint by selecting appropriate host luminescent agents and changing guest luminescent agents as dopants used in combination with the host luminescent agents. Dependently on the combinations of the host and guest luminescent agents, the brightness and the life expectancy of luminescence can be improved by a large margin. It is said that organic EL device is a theoretically-excellent luminescent device, because it gives luminescence in itself and information displaying means therewith are free of view angles and low in energy consumption because it needs no backlight.
Although, in organic EL device which gives luminescence in green region, there has been reported an improvement of luminescent efficiency by incorporating guest luminescent agents, but it has been found no guest luminescent agent which effectively allows organic EL device to give luminescence in red region and it still remains far from emitting a pure red luminescence, poor in life expectancy, and insufficient in both durability and reliability. For example, the organic EL devices disclosed in Japanese Patent Kokai No. 60,427/98 and U.S. Pat. No. 4,769,292 are insufficient in brightness and impure in red-color emission, and hence they have still problems in realizing full-color emission.
To supply organic EL devices at a lower cost, it is essential to find luminescent agents which do not intrinsically need doping by guest luminescent agents, make them simple the systematic structure of the organic EL devices and facilitating the step of vapor deposition in their preparations. Although various proposals have been made on luminescent agents in organic EL devices, there have been found no compound which fulfills the requirements as described above.
In view of the foregoing, the objects of the present invention are to provide organic compounds which absorb and/or emit lights in the visible region as well as to provide their uses in photochemical polymerization, organic EL devices, and dye lasers.
To solve the above objects, the present inventors eagerly screened compounds and researched and found that the pyran derivatives, which are obtainable through the step of reacting a compound having 4H-pyran skeleton with a compound having 3-formylcoumarin skeleton, have an absorption maximum in the visible region and substantially absorb visible light, and therefore they are very useful in photochemical polymerization. They also found that the pyran derivatives obtainable through such a step is very useful in dye lasers and organic EL devices because the pyran derivatives have the luminescent maxima in the visible region and emit visible light when excited.
More particularly, the present inventors confirmed that the pyran derivatives of the present invention emit at a high efficiency visible light, particularly, a light in red region when used in compounds for composing organic EL devices, in particular, when used in materials for composing luminescent layers of organic EL devices. The present invention was made on the basis of the creation of novel pyran derivatives and the findings of their industrially-useful features.